■ Study Notes: Electromagnetic Waves
Introduction
Electromagnetic (EM) waves are transverse waves consisting of oscillating electric (E) and magnetic
(B) fields.
Both fields are perpendicular to each other and to the direction of wave propagation.
EM waves do not require a medium; they travel in vacuum.
Properties of EM Waves
Speed in vacuum (c) = 3 × 10^8 m/s.
Relation between speed, wavelength, and frequency: c = λf.
Transverse nature: E ■ B ■ propagation direction.
They transport energy and momentum.
Maxwell’s Contribution
Maxwell predicted the existence of EM waves from his equations of electromagnetism.
EM waves are produced when accelerating charges generate time-varying E and B fields.
Generation of EM Waves
Produced by accelerating charges.
Examples: Radio transmitter antennas, vibrating electrons in atoms (light emission).
Electromagnetic Spectrum
Complete range of EM waves arranged by frequency or wavelength.
Order (low freq → high freq): Radio → Microwave → Infrared → Visible → Ultraviolet → X-rays →
Gamma rays.
Visible light range: ~400 nm (violet) to 700 nm (red).
Energy of EM Waves
Photon energy: E = hf, where h = Planck’s constant.
Higher frequency → higher energy.
Characteristics of Different Spectrum Regions
Radio waves: Communication, broadcasting.
Microwaves: Radar, cooking, satellite communication.
Infrared: Remote controls, thermal imaging.
Visible light: Human vision.
Ultraviolet: Sterilization, tanning.
X-rays: Medical imaging.
Gamma rays: Cancer treatment, nuclear reactions.
Polarization
EM waves can be polarized since they are transverse.
Polarization confirms transverse nature of EM waves.
Applications
Communication: Radio, TV, mobile phones.
Medical uses: X-rays, cancer therapy.
Scientific instruments: Spectroscopy, telescopes.
Everyday uses: Remote sensing, microwave ovens, solar panels.
Quick Summary Table
Spectrum Region Wavelength Range Applications
Radio Waves > 1 m Broadcasting, communication
Microwaves 1 mm – 1 m Radar, cooking, communication
Infrared 700 nm – 1 mm Thermal imaging, remote controls
Visible Light 400 – 700 nm Vision, optical instruments
Ultraviolet 10 – 400 nm Sterilization, tanning
X-rays 0.01 – 10 nm Medical imaging
Gamma Rays < 0.01 nm Cancer treatment, nuclear studies
